1. Field
This invention relates to brake systems. More particularly, it relates to a dual brake, self-cooling, fail-safe direct drive axle brake system mounted to a wheel end unit, such as a differential gearing system or an hydraulic drive motor, and a direct drive wheel. It is positioned to apply brake force at either low or high speeds, and employs a cooling system to effectively disperse heat build-up during braking.
2. State of the Art
A number of conventional brake systems for vehicles with and without separate cooling systems are known. For example, Blatt, U.S. Pat. No. 4,470,487 discloses a fail-safe brake for a drive shaft, which includes means by which the brakes are spring activated upon interruption of the source of pressure fluid. The Blatt invention engages brake pads adapted to operatively move against a flywheel attached to a sleeve journaled through bearings and keyed to the drive shaft. Blatt requires high pressures and large pressure pads to overcome the high torque of the flywheel. Richardson, U.S. Pat. No. 4,363,384, discloses a disc brake assembly for tractors carried within a differential housing immediately to the rear of a transmission housing. Richardson is mounted to the rear of the transmission which supports a disc brake adapted to engage discs on the output shaft of the transmission. It is used primarily as a disc parking brake, not as a service brake, because of the extreme torque which would have to be overcome at this position to stop the drive shaft. Schmitt, U.S. Pat. No. 4,491,202, discloses a disc brake assembly for heavy duty vehicles with interchangeable brake modules. Schmitt requires a liquid circulating in a closed circuit to cool the large braking discs conventionally mounted inside a rim of a wheel, because of the high torque generated in this wheel location.
Hause, U.S. Pat. No. 3,323,389 discloses a live axle having a final drive, a drive differential, and braking structure to control drive differential output. The position of the Hause braking system is such that it fails to take advantage of the lower axle torque before being increased by the wheel hub planetary drive ratio, and thus requires large brake pads. These large brake pads generate extreme heat, which must be dissipated with an elaborate liquid cooling system. Thompson et al., U.S. Pat. No. 4,377,094, is an example of a combination liquid cooled hydraulic disc brake and cooling system for a tracked vehicle which also requires an elaborate cooling system. The brake body is adapted for installation on the steering differential of a tracked vehicle in controllable braking engagement to one of the rotating braking axles. Thompson et al. requires large brake pads and a separate brake cooling system to minimize brake repairs. As the service brake components are not located near the ends of the track drive sprockets, peripheral access for brake repairs is more difficult.
Kolvunen, U.S. Pat. No. 3,814,222, is a final drive differential and brake mechanism for a vehicle in which the differential has two outputs, one for each drive axle. A disc brake pack is arranged to brake both outputs to provide a vehicle service brake. Again the brake disc pack is positioned to apply braking torque at a point after the torque has been increased by the wheel hub planetary, and therefore requires large brake pads and a separate cooling system. Chauveau et al., U.S. Pat. No. 4,566,563, is a hydraulically activated multi-plate disc type of brake journal mounted at the end of an axle of a vehicle to brake it through the intermediary of a reduction gear mechanism. Chauveau et al. also requires a cooling system to dispose of heat buildup, but better positions the brake assembly for easy access.
A number of integrated dual brake mechanisms are also known. Cronin, U.S. Pat. No. 4,667,784, discloses a dual brake mechanism for a vehicle having a first disc brake assembly associated with the first output drive member and a second disc brake assembly associated with an opposite second output drive member. Although Cronin provides a dual brake mechanism which can be compactly integrated with a steering differential and a secondary parking brake actuator, it does not attach the brake system directly to the axle at a point for braking before the wheel hub planetary increases the drive torque before applying the brakes. Morgan et al., U.S. Pat. No. 4,263,991, also discloses a combined fail-safe and service brake having the brake positioned between the motor drive and the gearbox as shown in FIG. 2.
Keese, U.S. Pat. No. 4,037,694 places multiple friction brakes at the out end of the planetary reduction system splined to the end of the shaft near the wheel hub, applying force after the torque of the shaft has been increased by the wheel hub planetary gearing system.
Chamberlain, U.S. Pat. No. 4,207,968 is a double disc type brake system including two disc packs respectively placed in a back to back relationship. Multiple pistons are positioned in a common actuator arrangement centrally disposed between the two disc packs to operate both disc packs. For light braking the piston actuates only the first disc pack. For heavier braking, both disc packs are actuated. Chamberlain has its brake housing operably interconnected to a sun gear in the double reduction final drive gearing assembly. Chamberlain therefore also applies its braking force after the torque of the shaft has been increased by the wheel hub planetary gearing system.
Jirousek et al., U.S. Pat. No. 4,391,351, discloses an inboard self lubricating manually activated emergency or parking brake for fork lifts with very small central hubs. The manually activated disc brake is directly attached to the wheel end of the shaft. To lubricate the Jirousek et al. disc brake, the shaft is surrounded by a tube actuator in communication with the differential to deliver lube oil from the differential to lubricate the disc brakes. The light weight Jirousek et al. manual fork lift brake is unsuited for use as a high speed service brake for large heavy duty vehicles having large brake drums which generate extreme heat build up during braking.
Co-pending "Inboard Self Cooling Three Function Fail Safe Brake System", Ser. No. 627,053, is an example of a self cooling inboard axle brake system positioned to apply braking force to vehicle traveling at low speeds under 25 mph to apply a brake force at points along the axle to take advantage of the smaller axle torque before being increased by the planetary drive gear ratio of the wheel hub. This brake system attached directly to the axle lacks bearing stabilization proximate the wheel end and is therefore subject to vibration at higher speeds, which interferes with the braking function.
Parker, U.S. Pat. No. 1,315,236, discloses a disc brake assembly adjacent to the differential assembly. Isbel et al., U.S. Pat. No. 3,102,608, provides separate disc braking assemblies for parking and service brake activation. Kovonagi, Japanese Patent No. 0223,342; Sidles, Jr. et al., U.S. Pat. No. 4,142,615, and Shinoda, U.S. Pat. No. 4,294,334, disclose various disc brake assemblies. Stritzel, U.S. Pat. No. 3,994,375, discloses another disc brake assembly. Klein, U.S. Pat. No. 4,327,414 discloses a sensor and ECU to achieve desired or predetermined braking in a system.
Cited for general interest are: Euler, U.S. Pat. No. 4,128,145, which is a combination fail-safe brake and one-way clutch particularly adapted for use with power trains for cranes; Jones et al., U.S. Pat. No. 3,995,722 provides a fail-safe actuator for a disc brake system particularly adapted for use with heavy duty disc brakes of railroad vehicles, automotive trucks, and airplanes; Daniels, U.S. Pat. No. 3,946,838, provides a fail-safe disc brake actuated with slant coil springs; Kendig, U.S. Pat. No. 2,998,101, discloses a safety brake for tandem axle trailers; Parker, U.S. Pat. No. 1,315,236 discloses an enclosed multiple-disk brake mechanism for tractors, which applies its braking force after the torque of the shaft has been increased by the wheel hub planetary gearing system; Windish et al., U.S. Pat. No. 4,560,034 provides a disc brake hydraulic control system having an automatic parking brake function when hydraulic pressure is below a certain operating level, a service brake function when pressure is above a predetermined operating level, and an emergency braking function upon loss of hydraulic pressure; and Winkler, U.S. Pat. No. 4,269,289, discloses a multiple liquid cooled friction disc brake which is low in direct and indirect parasitic energy consumption.
Co-pending "Improved Outboard Axle Brake System", Ser. No. 627,052 discloses a self-cooling hydraulic brake system positioned outboard between the planetary gear drive and wheel hub to apply brake force after the axle torque is increased by the planetary drive gear of the wheel hub for use with conventional or hydraulically driven wheel end brake designs. The invention requires critically sized brake components to insure proper heat dissipation of the heat generated during braking.
None of these inventions provides a self-cooling, dual brake, fail-safe, direct drive axle brake system utilizing easy access brake disk sub-assemblies positioned for use with conventional wheel end units for travel at low and high speeds. The invention, described below, provides such an invention.